"Two-phase" described 2 hot-wires that were 90(!!!) degrees out-of-phase.
It is demonstrably single-phase, as there is only one secondary coil. It just happens to have a 'center tap', which is at 'relative' zero potential.
The rest of Danny's dissertation is spot on. :)
Years? *SNORT* make that decades or *centuries*. expected lifetime of a light-bulb is approximately a 15th-order inverse relationship. Halve the voltage, and lifetime will be roughly 2**15th (32,768) times longer.
The 'lumens' (actually lumen-hours) of light output, per dollar of electricity supplied will be far, *FAR* inferior to the standard 120v bulb. There are standard "rough service" bulbs (lifetime for which is at a rated 130v) that are "close" to as dollar-efficient in energy usage as the 120v bulbs, but with a greatly improved lifespan. They don't cost much more than _quality_ 'standard 120v' bulbs, assuming you can find somebody that carries them.
[TELECOM Digest Editor's Note: Precisely! But a 25-watt bulb at 240 volts in a 120 volt fixture still presents a reasonably decent glow to point people in the direction they should walk to reach a fire escape, for example, which is I think how he was doing it. PAT]